Methods and devices for data projection

ABSTRACT

Provided are a device and method for data projection, in particular for windshields. A holographic element ( 11 ) is used here, in particular an imaging holographic element.

The present application relates to methods and devices for dataprojection, in particular for what are known as head-up displays (HUDs).The present application in particular relates to methods and devices ofthis type that may be used in vehicles, in particular in motor vehicles.However, the methods and devices described in this application can alsobe used for different applications, in particular in all transparentpanes. For example, the described methods and devices can also be usedin transparent panes of other vehicles, such as trains, buses, ships orplanes, or in real estate for windowpanes, if data projection is desiredhere.

Methods and devices for data projection are increasingly used to providedata to a user in a simple manner. The term “data” should here beunderstood in general terms, for example, projected data can compriseimages, videos, symbols, characters and/or numbers.

One area of application of such methods and devices for data projectionis the automotive field, for example for providing data to a handler ofa vehicle, for example a driver of a car, during driving. This can berealized, for example, by way of corresponding elements in a windshieldof a vehicle, as a result of which the driver does not need tospecifically direct his gaze onto a display, for example of aninstrument cluster, in order to obtain data, but can substantiallyperceive said data without substantially averting his gaze from theroad.

Such methods and devices are known, for example, generally from DE 102008 039 737 A1. That document proposes a holographic optical element ina windshield for providing a reflection for the human eye, wherein theconcepts in particular relating to inclined windshields of passengercars are explained.

Further examples of data projection which may be used for example alsofor car applications are known from WO 2014/115095 A2. Here, aholographic screen is used, and, depending on the distance of thisscreen from a human eye, a special contact lens is required to be ableto focus onto this screen in a simple manner.

It is therefore an object of the present application to provide improveddevices and methods for data projection.

Provided are a device as claimed in claim 1 and a method as claimed inclaim 24 and the use as claimed in claim 26. The dependent claims definefurther embodiments.

According to a first aspect, a device for data projection is provided,comprising: a holographic element to be arranged by, e.g. in or on, acarrier, and an imaging device that is adapted and arranged to transmitlight corresponding to data to be projected to the holographic element,wherein the holographic element is adapted to steer light received fromthe imaging device to a viewing site.

By using a hologram, in particular an imaging hologram, a compactstructure as possible.

The apparatus can be adapted to represent a three-dimensional object.

To this end, the imaging device can comprise an amplitude modulator anda phase modulator for generating three-dimensional images.

It is thus possible, in a comparatively simple manner, to providethree-dimensional objects, for example for control elements.

The holographic element can be adapted for imaging an image provided bythe imaging device onto at least one intermediate image which isviewable from the viewing site.

A distance between the intermediate image and the viewing site can herebe at least 2 m, but is not limited thereto.

The at least one intermediate image can comprise a real image. It isalso possible hereby for example for 2D or 3D images (or objects) to berepresented in a plane between the holographic element (or a display)and a viewer.

Additionally or alternatively, the at least one intermediate image cancomprise a virtual image.

The at least one intermediate image can comprise at least twointermediate images. In this way, representation in different planes, atdifferent sites or for different viewers is possible.

The at least two intermediate images can be arranged in particular atvarious distances from the holographic element, which corresponds to arepresentation in different planes.

The at least two intermediate images can also be viewable fromrespectively different viewing sites. For example, different contentscan be provided to different viewers (e.g. driver and front passenger),or the size of an available eyebox can be increased.

The holographic element can be adapted for generating a firstintermediate image of the at least two intermediate images on the basisof a first group of wavelengths, and a second intermediate image of theat least two intermediate images on the basis of a second group ofwavelengths that differ from the wavelengths of the first group. In thisway, separate color images can be generated.

The imaging device can comprise a first imaging system for generating afirst intermediate image of the at least two intermediate images and asecond imaging system (121) for generating a second intermediate imageof the at least two intermediate images, wherein the first imagingsystem and the second imaging system are arranged at different sites.Here, an angle selectivity of the holographic element is exploited.

The holographic element can also comprise a holographic diffusionscreen. In such a design, the hologram plane acts as a projection screenfor a defined wavelength and deflection angle range. Consequently, theuse of compact laser projectors is in particular made possible. In thiscase, the image is formed directly on the pane as a real image.

The device can furthermore comprise the carrier, wherein the carrier cancomprise a windshield which is arranged at an angle of <30°, for example<15° or equal to 15°, with respect to the perpendicular.

By adapting the holographic element to an approximately perpendicularcarrier (for example in the range of less than 30° with respect to theperpendicular), a simple application in trucks, buses and othervehicles, which have approximately perpendicular front panes, ispossible.

An angle between a chief ray of the light coming from the imaging devicein a direction of the holographic element and a perpendicular on thewindshield can here be between 40 and 80°.

The holographic element can be adapted to direct light, which isincident on the holographic element at a specific angle range, to theviewing site, and to be transparent for light outside the specific anglerange.

The holographic element can be adapted to be transparent for lightoutside one or more specified wavelength ranges, wherein the wavelengthranges can have in particular a spectral bandwidth of <20 nm or <10 nm.Within the one or more wavelength ranges, the holographic element canhave, for example, a high diffraction efficiency. The one or morewavelength ranges can then be used as operating wavelengths of a head-updisplay.

By way of using such a narrow band, a high transparency can inparticular be achieved for the largest portion of the visible light,despite the provision of the holographic element. The environmentimpression is not noticeably impacted by it.

The one or more wavelength ranges can comprise a wavelength in the redrange, a wavelength in the green range, and a wavelength in the bluerange. It is preferred here for wavelengths of this imaging device to betuned exactly to the wavelengths of the holographic element, for examplewith a deviation of less than 2 nm, which makes it possible for pixelsof different colors to be located laterally and exactly one on top ofthe other in the depth and thus for mixed colors, e.g. white, to begenerated relatively precisely. In the case of monochromatic use,greater deviations or a greater operating range (for example in therange of 30 nm) are possible. It is also possible for more than threesuch wavelengths to be used, for example to permit polychromaticoperation.

The one or more wavelength ranges can comprise a first group ofwavelength ranges and a second group of wavelength ranges, wherein theholographic element can be adapted to direct wavelengths of the firstgroup to a different viewing site than wavelengths of the second group.Representation of color images at different sites is thus possible.

In particular, the combination of operating wavelengths and a chiefdeflection direction can be realized in a targeted manner such that thereflection hologram in or on the pane blocks light from the environment,in particular from the main viewing directions of the vehicle handler,wherein the blocked wavelengths can correspond to those of commerciallaser pointers. In this design, the specifically adapted HUD isadditionally able to effectively reduce the risk of accidental ordeliberate glare or injury to the driver due to laser sources which arenot eye-safe.

The holographic element can be adapted to protect a viewer of theholographic element against external laser radiation.

The holographic element can have an imaging function.

The holographic element can be adapted—e.g. by way of suitable lightexposure—to a curvature of the carrier, e.g. a windshield.

According to a second aspect, a method for operating a device asdescribed above is provided, comprising:

illuminating the holographic element of the device, and

directing the light to the viewing site by way of the holographicelement.

Said illuminating can comprise illuminating with light of a redwavelength, a green wavelength, and a blue wavelength.

Provided according to a third aspect is the use of a holographic elementin a windshield for protecting against laser pointers.

Various embodiments of the present invention will be explained in moredetail below with reference to the attached drawings, in which:

FIG. 1 shows a schematic illustration of a device for data projectionaccording to an embodiment,

FIG. 2 shows an illustration of a device for data projection accordingto a further embodiment,

FIG. 3 shows an illustration of a device for data projection accordingto a further embodiment,

FIG. 4 shows a flow chart for demonstrating a method according to anembodiment,

FIG. 5 shows an illustration of a device for data projection accordingto a further embodiment,

FIG. 6 shows an illustration of a holographic element for protectionagainst laser radiation according to an embodiment,

FIG. 7 shows an illustration of a device for data projection accordingto a further embodiment,

FIG. 8A to FIG. 8C show illustrations for demonstrating the productionof a device according to an embodiment,

FIGS. 9A and 9B show illustrations for demonstrating the production ofthe device according to a further embodiment,

FIG. 10 shows a schematic illustration of a device for data projectionaccording to a further embodiment,

FIG. 11 shows a schematic illustration for demonstrating the productionof a device according to the embodiment of FIG. 10,

FIG. 12 shows a schematic illustration of a device for data projectionaccording to a further embodiment, and

FIG. 13 shows a schematic illustration of a 3D imaging device.

Various embodiments will be explained in detail below. These embodimentsserve only for illustrative purposes and are not to be interpreted asbeing limiting. By way of example, embodiments having a multiplicity offeatures, elements and details will be described, which should not beinterpreted as meaning that all these features, elements or details arenecessary for the implementation. Rather, it is possible in otherembodiments for some of the elements, features and details to be omittedand/or to be replaced by alternative features, elements and details.Elements, features and details of different embodiments can be combinedwith one another.

In embodiments, a holographic element for data projection is used. Theholographic element can in particular be wavelength-selective, forexample for a red, a green, and/or a blue wavelength, and be transparentfor other wavelengths.

FIG. 1 illustrates a device according to an embodiment. In theembodiment of FIG. 1, a holographic element 11 is mounted on a carrier10. The carrier 10 can be, in particular, a windshield of a vehicle. Ina preferred embodiment, the carrier 10 is an approximately perpendicularwindshield, for example a windshield which is inclined by at most 15° orat most 10° with respect to the perpendicular, as is used for example inbuses or trucks. Such windshields can in particular have curvatures. Theholographic element 11 is provided on or in the carrier 10. Theholographic element 11 can act, for example, as a diffusion screen, butcan also have an imaging effect for generating an intermediate image.Examples of this will be explained below with reference to FIGS. 2 and3.

The holographic element 11 can be wavelength-selective in a narrow band,i.e. have an imaging function and/or diffusion-screen function only forwavelengths within one or more narrow spectral ranges, while it remainstransparent for the remaining wavelengths. In this way, the holographicelement 11 is transparent for most wavelengths, and permits, forexample, a view through a windshield which serves as the carrier 10.Narrowband in this case can be understood to mean that a function of theholographic element applies only in one or more spectral ranges of awidth of <20 nm or <10 nm, in particular for specific wavelengths±aproduction-related tolerance.

In particular, a holographic function for a red, a blue, and a greenwavelength can be present, as a result of which projection of coloreddata becomes possible with simultaneous pellucidity for the greatestportion of the visible light.

The device of FIG. 1 furthermore comprises an imaging device 12 (alsoreferred to as imaging system below), which directs light, correspondingto data to be projected, toward the holographic element 11. In aholographic element 11 having a diffusion-screen function, the imagingdevice 12 can scan, for example, the holographic element 11 by way ofone or more laser beams (for example a red, a green, and/or a blue laserbeam). In a holographic element 11 having an imaging function forgenerating a virtual intermediate image, the imaging device 12 itselfcan have, for example, a diffusion screen, and the light correspondingto the light on the diffusion screen is directed to the holographicelement 11 in the form of light 13. In other embodiments, the imagingdevice 12 can also comprise, for example, a display such as an (O)LED,LCD or TFT display as an imaging element.

The holographic element 11 then directs the light 13 corresponding to aholographic function of the holographic element 11, in the form of light14, to an eye 15 of a viewer, as a result of which the viewer can viewthe projected data.

As has already been explained in the introductory part, the term “data”should here be understood in wide terms and can refer to any number ofsymbols, letters, numbers, images, videos and/or combinations thereof.

By way of the use of the holographic element 11, in particular animaging holographic element, the installation space required for thedata projection can be reduced. In particular, imaging properties of thehologram 11 can be selected such that further imaging elements, forexample for magnification, such as for example free-form mirrors orlenses, and/or elements for beam folding are not necessary.

FIG. 2 shows a device for data projection according to an embodiment.The embodiment of FIG. 2 serves for projecting data into a windshield20, which serves as a carrier for a holographic element 25. In theillustrated embodiment, the windshield 20 is inclined. In otherembodiments, the windshield 20 can be perpendicular or approximatelyperpendicular, as is the case e.g. in a windshield of a truck or a bus.

A holographic element 25 is arranged on or in the windshield 20. Theholographic element 25 can in particular comprise a volume hologram, inwhich an imaging function was holographed in one or more layers. In apreferred embodiment, this function can in particular be holographed forthree discrete wavelengths in the red, blue and green ranges, such thatthe holographic element 25 has, as described below, an imaging functionfor these three wavelengths, while it is transparent for otherwavelengths and thus in particular permits the view through thewindshield.

An imaging device 21 illuminates, as indicated by a ray 22, theholographic element 25 with an image to be represented corresponding tothe data to be projected. The image to be represented can be generated,for example, by scanning a diffusion screen with one or more lasers orby way of a display apparatus, such as an LCD display, a TFT display ora light-emitting diode (LED) display (for example on the basis oforganic light emitting diodes (OLEDs)).

The holographic element 25 is here illuminated with the image at anangle with respect to a perpendicular 23 on the windshield 20, whereinthe angle can depend on a configuration of the holographic element 25.In particular, the holographic element 25 shows in some embodiments animaging function only for one or more specific incidence angles (forexample between the light ray 22 and the perpendicular 23), while it istransparent for other angles.

In the embodiment of FIG. 2, the holographic element 25 images thereceived image onto a virtual image 25. The virtual image 25 is, asindicated by way of rays 26, represented for an eyebox of a viewer's eye27.

The angle at which the virtual image 25 appears for the eye 27 herediffers from the angle at which the image, corresponding to the ray 22,falls onto the holographic element 25. The participating angles can beadapted by way of the design of the respective holographic element 25.In particular, the participating angles can be taken into considerationduring the light exposure of the hologram as can a curvature of thewindshield 20.

The function of the holographic element in specific embodiments thusbecomes effective only for one or more selected wavelengths and only forthe incidence at one or more angles, because a Bragg condition has beenmet only for these angles and wavelength, for example. Light of adifferent color passes through the holographic element without beingobstructed, such that the pane in this case is transparent.

The embodiment of FIG. 2 can thus be simply adapted to many differentwindshields and can be used in particular for approximatelyperpendicular windshields.

With preference, the virtual image 25 is imaged at a distance of >2 m,with more preference >4 m, in particular >6 m or >8 m, from the eye 27.In this way, no change or only minor change in the focus of the eye 27between viewing for example of a road through the windshield 20 andviewing the virtual image 25 is necessary. This can facilitate viewingof the virtual image 25 and thus of the projected data, and can be, forexample, less tiring for an eye than in cases in which it is necessaryto constantly switch focus between a near virtual image and the road. Inother embodiments, the virtual image can also be generated at a distanceof <2 m.

In the embodiment of FIG. 2, for example an angle between the ray 22 andthe perpendicular 23 can be in the range of 35°, the windshield can beat an angle of 30° with respect to the horizontal, and a distance of theeye 27 from the windshield can be approximately 80 cm. A viewing anglefor the virtual image 25 can be in the range of 5°-7°, and the viewingof the image 25 can be performed at an angle of approximately 65° withrespect to the perpendicular on the windshield. For a light exposuresetup, corresponding angles can then be selected for the exposure of thehologram.

FIG. 5 illustrates a device similar to the device of FIG. 2 for the caseof a perpendicular windshield. The windshield is here designated with50, while 51 designates a position of a corresponding holographicelement. An imaging device 52 illuminates the holographic element 51 atan angle α between a chief ray from the imaging device 52 to theholographic element 51 and a perpendicular on the windshield 50, forexample between 40 and 80°, with an image that corresponds to data to beprojected. The holographic element 51 images this image in virtuallymagnified fashion, wherein the virtual image 53 can be viewed by an eye54 in an eyebox. The use of the holographic element 51 here offers theadvantage, compared for example to projection head-up displays, thatillumination can take place at a substantially arbitrary angle α (e.g.between 40 and 80°) and viewing can occur near the normal, with theresult that here the angle of incidence and the emission angle candiffer. The imaging device 52 can here be arranged, for example, in aposition above (as shown) or below the windshield. Correspondingconfigurations are also possible with holographic diffusion screens, aswill be described in more detail below.

It is thus possible to set up a device for data projection for vehicleshaving perpendicular windshields, such as busses, trucks or commercialvehicles, for which, up until now, there has been no possibility of ahead-up display by way of conventional projection solutions.

FIG. 3 illustrates a device according to a further embodiment. In theembodiment of FIG. 3, a holographic element 33 is again provided in awindshield 30. The holographic element 33 has, in the embodiment of FIG.3, a diffusion-screen function (also referred to as a holographicdiffusion screen). This diffusion-screen function can again be realizedin particular for specific angles of incidence of incident light 32 to aperpendicular 36 and for specific wavelengths, preferably a red, agreen, and/or a blue wavelength. For other wavelengths or angles, theholographic element 33 can be transparent.

By providing a diffusion-screen function, no intermediate image needs tobe generated. The holographic element can be directly illuminated, inparticular scanned, for example, by way of a laser light source 31.Here, the image construction occurs, for example as in conventionalcathode ray tubes, through line-wise, fast deflection of a light point.The light point in the present case is generally formed by a laser focusand is modulated temporally during the deflection movement in terms ofits brightness such that, on account of time averaging within a timeinterval that the human eye can no longer resolve, the image impressionis obtained.

In an embodiment, the laser light source 31 has three different lasersof red, green, and blue color, with which the holographic element 33 canbe scanned such that color representation is possible. However, othertypes of polychromatic image generation are possible, i.e. imagegeneration with a plurality of colors. For example, displaypossibilities using a micromirror device (DMD, Digital MicromirrorDevice) or a liquid-crystal device (for example LCoS, Liquid

Crystal On Silicon) can be used with temporal triggering. The entireimage is here represented successively in the individual colors, withthe time sequence of the representation being so quick that the viewersees only the polychromatic image with the desired image coloring.

For polychromatic image representation, it is important here for typicalholographic elements that the wavelengths of the image generation (forexample red, green, and blue wavelength) are adapted exactly to theoperating wavelengths of the holographic element. Typically, thedeviation between the wavelengths used and the operating wavelengths ofthe holographic element should be no more than 2 nm. If greaterdeviations occur, green, red, and blue pixels of the virtual image mayno longer be located exactly one on top of the other and thus no correctcolor mixing takes place. With more accurate tuning, by contrast, thepixels for the different colors are located one on top of the other, andsubstantially any desired color, for example white or yellow, can begenerated.

In other embodiments, however, monochromatic representation can also beused, in particular if it is sufficient for a specific application (forexample representation of texts or numbers). In this case, exact tuningof the wavelengths is not necessary, and the holographic element can bedesigned for example for a comparatively wide operating range in a rangeof, for example, 30 nm. The light generated by the imaging system thenonly has to be located within this operating range to generate an imagewith the lowest possible distortion.

As indicated by rays 34, the image projected onto the holographicelement 33, which acts as a diffusion screen, can then be viewed by aneye 35 at an angle to the perpendicular 37. The site of origin of thelight for a specific pixel is here determined by the interaction of thelaser projector with the geometry of the pane. A low-distortion imagecan be perceived in a specific spatial region (eyebox). In a preferredembodiment, the hologram can be configured locally such that thedeflection function of the laser beam can be effected with adequatediffraction efficiency, i.e. the Bragg condition is met at all sitesthat contribute to the formation of an image. As a result, in theembodiment of FIG. 3, a possible curvature of the windshield 30 is takeninto consideration in the holographic element 33.

Instead of a laser light source, other light sources can also be usedfor illumination, for example broadband sources such as a halogen lampin combination with an imaging system.

In the embodiment of FIG. 3, angle of incidence and emission angle ofthe diffusion screen can also be selected substantially arbitrarily suchthat an arrangement similar to the arrangement of FIG. 5, adapted toperpendicular windshields, is possible.

In the embodiment illustrated, it is possible in particular to dispensewith further optical elements, which permits a compact construction, anda construction is possible e.g. only with an imaging device and aholographic element in or on a windshield.

Tuning the operating wavelengths and the local deflection function of aholographic element used can, in some embodiments, in addition to thefunction of data projection, provide a protecting function against thelight of the nowadays commonly used laser pointers. To this end, theholographic elements already discussed are adapted such that theorientation of the Bragg planes in the hologram layer that ensure thedeflection of the data beam path permit blocking of the ingress of lightof specific wavelengths (e.g. 532 nm, 640 nm, 450 nm, 405 nm). By way ofthe preferred configuration of the hologram structures in the form ofreflection holograms, the optical blocking action takes place similar toin a dielectric layer system by way of reflection back toward theoutside. The distance between the Bragg planes must be configured suchthat a phase delay of the partial reflections at neighboring Braggplanes of a laser pointer wavelength occurs along the optical path ofthe beam inside the material. When using volume hologram material with acomparatively large refractive index difference (approximately 0.03) anda comparatively low layer thickness (approximately 10 μm), it ispossible to achieve good suppression of the laser light from the outsidewithin an extended angle range (approximately±10 . . . 30°. The bestlaser projection exists, for example, for viewing directions runningexactly toward the represented image content for exactly the wavelengthwith which the holographic element operates.

For a construction as is shown in FIG. 2 or FIG. 5, this will beexplained by way of the example of FIG. 6. A holographic element isdesignated with 60. A holographic element of this type can contain amultiplicity of Bragg planes 65, i.e. planes having slightly differentoptical refractive indexes, which, in sum, act as selective mirrors,adapted to the pointer wavelengths. An incident beam from an imagingdevice is designated with 61, which is diffracted as the beam 62 andsteered toward a viewer's eye (e.g. as explained with reference to FIG.3). A normal on the holographic element 60 is designated with 66.

For corresponding wavelengths for which the holographic element isdesigned, a reflection function can additionally be achieved asprotection against a laser beam 63 which is incident from the outsideand is substantially reflected (diffracted) as a laser beam 64. Theholographic element 60 can be tuned to wavelengths of laser pointers(for example red, green, or blue semiconductor lasers). Such wavelengthscan be integrated, in addition to the already mentioned wavelengths forthe data projection, into the design of the holographic element 60. Inthis way, a combined function of data display and laser protection(function integration) of the device is obtained, without additionaloptically effective elements other than the holographic element (alsoreferred to as combiner hologram). The driver or pilot or viewer wouldthus be protected by the display with respect to the main viewingdirections. In order to adapt this protective function to differentconfigurations of the display system, it is possible to exploit the factthat Bragg gratings, which were designed for a specific angle and aspecific wavelength, can efficiently diffract a different wavelength ata different angle.

If the design of the device on the basis of different aspects takesplace in a manner such that the main angle of incidence of the objectwave starting from the imaging system with respect to the normal vectorof the Bragg planes of the grating is for example significantly lowerthan the expected angle of incidence of a laser pointer, for example bymore than 10°, then the operating wavelength of the holographic elementfor displaying data must in this case be reduced correspondingly withrespect to that of the laser pointer (and vice versa). In this way, itwould again be possible for the above-mentioned condition with respectto the appropriate phase delay of the partial reflections at the Braggplanes for the laser pointer wavelength to be attained.

FIG. 7 illustrates a corresponding laser projection function for thecase of a holographic diffusion screen (according to the embodiment ofFIG. 3). A windshield is designated with 70 and has a holographicdiffusion screen 71. As has already been explained with reference toFIG. 3, the holographic diffusion screen 71 can be scanned with lightfrom an imaging device 72, in particular a scanning laser light sourcewith one or more wavelengths, in order to provide data to be projectedfor an eye/both eyes 73.

If light is incident from the external side, the holographic diffusionscreen in the embodiment of FIG. 7 provides a protective function. Tothis end, the holographic diffusion screen 71 in the embodimentillustrated is tuned, as described above, to corresponding wavelengths.By way of example, in FIG. 7, an incident laser beam 74 is diffuselyscattered by the holographic element 71, i.e. the holographic diffusionscreen.

Since commercially available laser pointers have comparatively fewpossible wavelengths, these wavelengths can relatively simply be addedto the design of the respectively used holographic element for theprotection against laser pointers, without significantly affecting thetransparency of, for example, a windshield overall.

FIG. 4 shows a flowchart for demonstrating a method according to anembodiment. The method of FIG. 4 can be used in particular for operatingthe devices of FIGS. 1-3.

In a step 40, a holographic element is illuminated with light in threespectral colors, for example red, green and blue (rgb), wherein theholographic element is preferably transparent for other wavelengths. Instep 41, the holographic element then directs the light toward a viewingsite, wherein the holographic element to this end can image the lightonto an intermediate image, which is viewed from the viewing site (forexample as shown in FIG. 2), or the holographic element can serve as adiffusion screen (for example as shown in FIG. 3).

The production of holographic elements according to embodiments will nowbe explained below with reference to FIGS. 8 and 9.

FIG. 8A illustrates light exposure of a holographic element 82 for dataprojection purposes, for example according to the embodiment of FIG. 2.Here, for generating a holographic element 82, interference of twoopposite spherical waves, which can for example be generated using acoherent laser having a sufficient coherence length, is recorded on theholographic element 82, in particular within a holographic layer. Apoint light source 80 for emitting one of the spherical waves is herelocated at the later site of the imaging device and emits what is knownas a reference wave, and a further point light source 81 for emittingthe other of the spherical waves is located at the site of the latervirtual image and emits what is known as a signal wave.

By way of the distance of the two point light sources 80, 81 from theholographic element 82 during the exposure, the later distance of theimaging device from the holographic element 82 and the distance of thelater represented virtual image are fixed. If, for example, the pointlight source 81 is at a distance of 8 m from the holographic element 82,then later, during playback, the virtual image will likewise be locatedat a distance of 8 m from the holographic element 82.

The distance of the virtual image from the eyebox (i.e. substantiallyfrom a viewer's eye), will later correspondingly be at leastapproximately the sum of the distance of the point light source 80 fromthe holographic element 82, plus the distance of the point light source81 from the holographic element 82. It is thus possible in principle toimplement any desired distance of the virtual image during later use.

FIG. 8B here shows the application of the holographic element exposed asin FIG. 8A in an “ideal case.” The holographic element is illuminatedstarting from a point light source 83 (corresponding to an imagingdevice) with reference light, which results in the formation of avirtual image 84 (corresponding to the position of the point lightsource 81 in FIG. 8A), which can be viewed by an eye (eyebox) at 85.

FIG. 8C then shows a real application case. Here, during use, instead ofthe point light source 83, an imaging device 86 is used, which, asopposed to a point light source, has an extent Δy in the y-direction andan extent Δx in the x-direction. This can result in distortions withrespect to the ideal case of FIG. 8B, which are, however, negligible toa certain degree for practical applications, depending on a desiredimage quality. With preference, here the extent of the imaging device isselected to be comparatively small, and the imaging device is arrangedin the vicinity of the site of the point light source 80.

FIGS. 9A and 9B show a further case in which a distance “infinite” ofthe virtual image from a viewer is implemented.

FIG. 9A here illustrates the light exposure of a holographic element 90.A reference wave 92 is generated by a substantially point-type signalsource 91, corresponding to the signal source 80 of FIG. 8A. Instead ofa second point-type signal source for generating the signal wave, here asignal wave 93 with a parallel pencil of rays is used, which can begenerated for example by a collimated broadened laser beam.

FIG. 9B shows the application of the holographic element 90, which hasbeen exposed as illustrated in FIG. 9. An imaging device 95 (in theideal case a point-type source, in the real case a source as illustratedin FIG. 8C) illuminates the holographic element 90 from a position whichcorresponds to a position of the signal source 91. This results in thegeneration of a virtual image at infinity corresponding to light rays94, which can be viewed at a site 96.

Production of a holographic element as a diffusion screen can beeffected according to FIG. 8A, where in this case the signal wave isgenerated by a diffusion screen (instead of by the signal source 81),which is located in the vicinity of the holographic element. Theholographic diffusion screen is thus recorded in embodiments as areflection hologram. The form and location of the reference sourceremain intact, i.e. can be selected like the signal source 80 of FIG. 8Aat a suitable angle with respect to the respective holographic elementin order to later achieve a suitable arrangement adapted to a respectiveinstallation space.

In the embodiments which have been discussed thus far, a virtual imageis generated by way of a holographic element and a corresponding imagingdevice. In other embodiments, a real image can also be generated.Corresponding embodiments will now be explained with reference to FIGS.10 and 11.

A corresponding modification, i.e. provision of a real image instead ofa virtual image, can be effected in all discussed embodiments as long asthere is sufficient space between the viewer and the holographic elementfor generating the real image. In particular, in these embodiments, thereal image is generated between the viewer and the holographic element.Such devices are suitable, for example, for representing controlelements, which can then be operated by the viewer, wherein conventionaldevices for gesture recognition (for example camera, distance sensorsand the like) can be used to detect the operation. During the operationof the thus produced control element, the representation of the controlelement (for example head or rotary switch) can be changed according tothe operation, for example turning of the rotary switch can beillustrated.

FIG. 10 illustrates an embodiment of a corresponding device. The deviceof FIG. 10 comprises an imaging device 100, which can be configured likethe imaging device in the above-discussed embodiments, and a holographicelement 101. In the case of illumination by way of the imaging device100, the holographic element 101 generates a real image at a site 102,which can be viewed within a box 103. Here, the real image 102 is thusgenerated between the viewer (at 103) and the holographic element 101.

FIG. 11 illustrates a production process for the holographic element 101of FIG. 10. For the production, a holographic material, as alreadydiscussed above, is exposed to a reference beam (or a reference wave)111, which diverges starting from a site 112. The site 112 herecorresponds to the site where later the imaging system 100 will bearranged. At the same time, the holographic material is exposed to asignal beam (an object wave) 110, which converges toward the site 102 ofthe real image. As already explained, this exposure can occur separatelyfor different wavelengths, for example a red, a green, and a bluewavelength.

It should be noted that mixed forms are also possible, in which both avirtual image and a real image are generated, for example with differentcombined volume holograms.

In the embodiments which have been discussed thus far, a virtual or realimage is represented in one plane. In other embodiments, imagerepresentation (virtual and/or real) can also be effected in a pluralityof planes, at different angles and/or generally at different sites. Itis possible here to exploit the fact that the holographic elements used,in particular volume holograms, operate, as already described, in bothwavelength-selective and angle-selective fashion. It is thus possiblefor different colors to be imaged to different sites and/or be viewedfrom different angles, by selecting, for example, the directions andforms of reference beam and the signal beam for different wavelengthsduring the production of the holographic element.

It is in particular possible to generate color images (real or virtual)at different sites by way of red, green and blue wavelengths, whichdiffer in terms of the wavelength by more than one sensitivity range ofthe respectively used hologram. For example, the operating wavelengths532 nm (green), 460 nm (blue) and 660 nm (red) can be used for a firstimage, while the operating wavelengths 520 nm (green), 442 nm (blue) and647 nm (red) can be used for a second image. By combining correspondingvolume holograms, it is thus possible hereby for example to generate afirst virtual image at a first distance from the holographic element,for example 1 m, and a second image at a second distance, for example 5m, wherein for each of these images a polychromatic representation,including white, is possible. A similar case can also be implemented formonochromatic images with in each case only one wavelength. The imagegeneration can be implemented with a single imaging system, which inthat case generates a total of 6 different colors, or with separateimaging systems which can also be arranged at different angles. A viewerin the eyebox then sees both contents at different distances. Here, eachholographic element only sees “its own” operating wavelengths and isotherwise transparent. Combinations with even more wavelengths anddifferent distances are also possible.

In embodiments in which the imaging systems are arranged at differentsites, it is also possible to use the same wavelengths for both images,since, as mentioned, the holographic elements are also angle-selective.A corresponding embodiment is illustrated in FIG. 12.

In the embodiment of FIG. 12, a holographic element 122 contains volumeholograms for two different imaging systems 120, 121. A virtual image isgenerated at a site 123 on the basis of light from the imaging system120, and a virtual image is generated at a site 124, which has adifferent distance from the holographic element 122 than the site 122,on the basis of light from the imaging system 121. The two virtualimages can then be viewed within an eyebox 125. The projection of thevolume holograms for the two imaging systems 120, 121 can be effected ineach case as described above in separate layers.

In the example illustrated in FIG. 12, the virtual images can be viewedat the sites 123, 124 from the same eyebox 125, i.e. simultaneously.However, other variations are also possible. For example, theholographic element 122 and the imaging systems 120 and 121 can beadapted such that the virtual images can be observed “next to oneanother,” as it were, which can effectively increase the size of theeyebox. The configuration can also be such that separate images can beviewed from different positions, for example from a driver position anda front passenger position in a vehicle. In this way, different contentscan be represented for different persons. It is thus possible overall toprovide different virtual or real images by way of one or more imagingsystems, possibly with different operating wavelengths, at differentsites and/or for viewing from different sites.

In the above-discussed embodiments, a planar virtual or real image isgenerated by way of an imaging system device and a holographic element.In other embodiments, three-dimensional contents (3D contents) can alsobe represented.

In some embodiments, similar as described above, separate virtual orreal images are generated for this purpose for the left and the righteye in correspondingly small eye boxes. If the images arecorrespondingly selected with different perspectives, a stereo effectcan thus be brought about.

In other embodiments, a 3D imaging system can be used, as a result ofwhich the representation of true virtual or real three-dimensionalimages is made possible. A corresponding imaging system is schematicallyillustrated in FIG. 13.

The imaging system of FIG. 13 comprises a surface light source 130, aspatial amplitude modulator 131 and a spatial phase modulator 132. Thespatial amplitude modulator 131 can be used to modulate light generatedby the light source 130 in a location-selective manner with respect tothe amplitude. Examples of such spatial amplitude moderators are forexample LCDs, micromirror devices (DMDs) or LCoS arrangements.

The spatial phase modulator 132 can correspondingly be used to modulatethe phase of the generated light in a spatially resolved fashion.Corresponding spatial phase modulators are likewise commerciallyavailable and can be based, for example, on liquid-crystal technology(e.g. LCoS). It is thus possible to modulate the generated light bothwith respect to the amplitude and with respect to the phase. Since a 3Dimpression is brought about in particular by way of different phases ofthe light that reaches the eye, it is possible with such an arrangementto generate a three-dimensional image. The light source 130 can herealso be operated by scanning (for example by way of lasers) to a certainextent, and can have different colors (for example red, green, blue) fora color representation. The imaging system illustrated in FIG. 13 can bearranged at the positions of the imaging systems of the previouslydiscussed embodiments. In the embodiment of FIG. 8C, the artificiallygenerated spatial 3D object is then located in the source point of thereference beam during the recording (reference sign 86 in FIG. 8C) andcan thus be reproduced as a 3D object increased in terms of size in thesource point of the signal source (reference sign 84 in FIG. 8C) for therespective eyebox. The representation of three-dimensional objects isconsequently also possible. Such three-dimensional objects can also beas explained above and used for representing control elements.

By using the illustrated solutions, a high degree of design freedom canbe achieved, since less installation space is needed, and in particularalso a location of an imaging device can be chosen freely within widelimits. The realization of large-area devices for data projection issimplified, since even in the case of devices having a large viewingfield for data projection, no more installation space or hardly any moreinstallation space is required than in small devices (only the size ofthe holographic element is increased—but applies only to diffusionscreen variant with low pane curvature+small viewing angles with respectto the pane normal). In addition, simple solutions for perpendicularwindshields are provided. A holographic element which is integrated in awindshield is also robust, for example with respect to solar radiation.An optimum protective function against laser pointer radiation from theoutside is possible with a targeted design for the majority of designs.

The embodiments illustrated serve merely for illustrative purposes andare not to be interpreted as limiting.

1. A device for data projection, comprising: a holographic element bearranged by a carrier, and an imaging device which is adapted andarranged to transmit light, corresponding to data to be projected, tothe holographic element, wherein the holographic element is adapted todirect light received by the imaging device to a viewing site.
 2. Thedevice as claimed in claim 1, wherein the device is adapted to representa three-dimensional object.
 3. The device as claimed in claim 2, whereinthe imaging device comprises an amplitude modulator and a phasemodulator for generating three-dimensional images.
 4. The device asclaimed in claim 1, wherein the holographic element is adapted forimaging an image provided by the imaging device on at least oneintermediate image that is viewable from the viewing site.
 5. The deviceas claimed in claim 4, wherein the at least one intermediate imagecomprises a real image.
 6. The device as claimed in claim 4, wherein theat least one intermediate image comprises a virtual image.
 7. The deviceas claimed in claim 4, wherein a distance of the intermediate image fromthe viewing site is at least 2 m.
 8. The device as claimed in claim 4,wherein the at least one intermediate image comprises at least twointermediate images.
 9. The device as claimed in claim 8, wherein the atleast two intermediate images are arranged at different distances fromthe holographic element.
 10. The device as claimed in claim 8, whereinthe at least two intermediate images are viewable from in each casedifferent viewing sites.
 11. The device as claimed in claim 8, whereinthe holographic element is adapted to generate a first intermediateimage of the at least two intermediate images on the basis of a firstgroup of wavelengths, and a second intermediate image of the at leasttwo intermediate images on the basis of a second group of wavelengths,which differ from the wavelengths of the first group.
 12. The device asclaimed in claim 8, wherein the imaging device comprises a first imagingsystem for generating a first intermediate image of the at least twointermediate images, and a second imaging system for generating a secondintermediate image of the at least two intermediate images, wherein thefirst imaging system and the second imaging system are arranged atdifferent sites.
 13. The device as claimed in claim 1, wherein theholographic element comprises a holographic diffusing screen.
 14. Thedevice as claimed in claim 1, further comprising the carrier, whereinthe carrier comprises a windshield that is arranged at an angle <15°with respect to the perpendicular.
 15. The device as claimed in claim14, wherein an angle between a chief ray from the imaging device to theholographic element and a perpendicular on the windshield is between 40and 80°.
 16. The device as claimed in claim 1, wherein the holographicelement is adapted to direct light, which is incident on the holographicelement at a specific angle range, to the viewing site and to betransparent for light outside the specific angle range.
 17. The deviceas claimed in claim 1, wherein the holographic element is adapted to betransparent for light outside one or more specified wavelength ranges.18. The device as claimed in claim 17, wherein the one or morewavelength ranges comprise a wavelength in the red range, a wavelengthin the green range, and/or a wavelength in the blue range.
 19. Thedevice as claimed in claim 17, wherein a width of the wavelength rangesis <20 nm, in particular <10 nm.
 20. The device as claimed in claim 17,wherein the one or more wavelength ranges comprise a first group ofwavelength ranges and a second group of wavelength ranges, wherein theholographic element is adapted to direct wavelengths of the first groupto a different viewing site than wavelengths of the second group. 21.The device as claimed in claim 1, wherein the holographic element has animaging function.
 22. The device as claimed in claim 1, wherein theholographic element is adapted to a curvature of the carrier.
 23. Thedevice as claimed in claim 1, wherein the holographic element is adaptedto protect a viewer of the holographic element against external laserradiation.
 24. A method for operating a device as claimed in claim 1,comprising: illuminating the holographic element of the device, anddirecting the light to the viewing site by way of the holographicelement.
 25. The method as claimed in claim 13, wherein saidilluminating comprises illuminating with light of at least one redwavelength, at least one green wavelength, and/or at least one bluewavelength.
 26. A use of a holographic element in a windshield for theprotection against laser pointers.